Method of controlling the alkalinity of alkali metal phenates

ABSTRACT

In a process for the spray drying of alkali metal phenates the carbon dioxide content of the gases leaving the drying chamber serves as an indication of the alkalinity of the product.

Inventor Appl. No.

Filed Patented Assignee United Sta-tes Pa-tent Gonzalo D. Milianl-lasbrouck, NJ.

May 19, 1969 Jan. 12, 1971 Tenneco Chemicals, Inc. a corporation ofDelaware METHOD OF CONTROLLING THE ALKALINITY or ALKALI METAL PHENATES 6Claims, 1 Drawing Fig.

us. c1 159/48, 260/621;23/232 Field ofSearch 159/48, 30;

[5 6] References Cited UNITED STATES PATENTS 2,193,336 3/1940 Lecher260/621 3,023,252 2/1962 Senior,Jr. 260/621 3,152,005 10/1964 Tuttle117/100 3,314,280 4/1967 Bumsetal... 23/232 Primary Examiner-NormanYudkoff Assistant Examiner-J. Sofer Attorneys-Daniel J. Reardon, GeorgeE. Lilly and Evelyn Berlow ABSTRACT: In a process for the spray dryingof alkali meta1 phenates the carbon dioxide content of the gases leavingthe drying chamber serves as an indication of the alkalinity of theproduct.

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i ia-Marie PATENIEU JAN 12 I9?! SAMPLE GAS-Z09 3% 5 VACUUM PUMP (01 1ANALYZER kfCORDER h J r34 jjv was TAN/(5 3 /3 $44 P/lf/VOL r FAN r MIXER74! 2! M I -23 FAN SCRUBBER v I g M 2/) ZZ-cYcwM METHOD OF CONTROLLINGTHE ALKALINITY OF ALKALIMETAL PHENAT-ES This invention relates to aprocess for the recovery of alkali metal salts from aqueous solutionsthereof. More particularly, it relates to a process for the productionof substantially anhydrous alkali metal phenates and carboxylates thathave uniform low alkalinity.

Alkali metal phenates are used commercially. in the production ofhydroxyaromatic acids by the Kolbe process. In this process the alkalimetal phenates are reacted with carbon dioxide under pressure and in theabsence of water toproduce salicylic acid, p-hydroxybenzoic acid, andother hydroxyaromatic acids. The alkali metal phenate starting materialis generally prepared by the reaction of a phenol with an alkali metalhydroxide in aqueous solution. Various methods have been proposed forthe recovery ofthe alkalirmetal salts in substantially anhydrous form,butnone has given entirely satisfactory results. For example, when anaqueous solution of an alkali metal phenate is dried in pans, the dryingmust'be carried out at relatively low temperatures because rigorousheating causes decomposition and discoloration of the product. Theresulting product, which contains small amounts of water, tends to cakeand must be ground before it can be usedindustrially. A process for thespray dryingof alkali metalphenate solutions under prescribedconditions-is disclosed in copending US. Pat. application Ser. No. 584,576 which wasfiled by Dege and Cheremisinoff on Oct. 5, 1966 Thisprocess results in the rapid drying of the alkali metal phenate and inthe formation of a finely divided product. Because product decompositionduring and after drying results when excessphenol is present in theaqueous alkali metal phenate solution, this process is usually carriedout using feed solutions that contain about 1 percent to 3 percentexcess alkali metal hydroxide. The presence of these amounts of excessalkali has been found to adversely affect the yield when the alkalimetal phenate is carboxylated. Forexample, when the sodium phenatethatis carboxylated contains 0.5 percent excess sodium hydroxide aconversion of 85 percent and a yield of 91 percent of salicylic acid areobtained, whereas when 1.0 percent excess sodium hydroxide is presentthe conversionis 80 percent and the yield is 88 percent, and when 2percent excess sodium hydroxide is present the conversion is about 70percent and the yield is about 80 percent.

In the spray drying processes carried out heretofore, the alkali metalphenate feed solutions have been prepared by a process in which therequired amounts of a phenol and an aqueous solution of an alkali metalhydroxide are placed in separate weigh tanks and then emptied into a mixtank. After mixing, the alkali metal phenate, solution is dischargedinto the spray dryer feed tank which is large enough to hold about tenof the mix tank batches. The feed solution is analyzed at regularintervals to make certain that it has the required composition. When theproportions of phenol and alkali metal hydroxide in the solution areincorrect as the result of malfunctioning of the weighing system,spillage, the use of recovered phenol containing excessive amounts ofimpurities,.and the like, the necessary adjustments are made in theamounts of phenolor alkali metal solution that are being used in thepreparation of the spray dryer feed solution. Because chemical analysisof the feed solution is time consuming and cannot be completed in lessthan about 2 hours, it is ordinarily carried out no more frequently thanonce or twice a day. In addition analysis by chemical procedures isreproducible only to within about i 0.5 molar percent of either alkalimetal hydroxide or phenol. To avoid the possibility that an excess ofphenol will be presentat any time in-the feed solution, itis customaryto use at least about 0.5 percent excess alkali metalhydroxide in thespray dryerfeed solution, and excesses of about '1 percent to 3 percentof alkalimctal hydroxide have usually been used.

As has been indicated hereinbefore, the presence of these relativelylarge excesses of alkali metal hydroxide in the spray dryer feedsolution results-in a sizeable decrease in the .yield of phenate iscarboxylated. ln addition, when more than about 0.5 percent of excessalkali metal hydroxide is present in the alkali metal phenate, theproduct is somewhat hygroscopic and vdilficult to dry, and the spraydried product contains more than the desired amount ofwater. Like the.presence of .excess alkali metal hydroxide, the presence of water inthe alkali metal phenate adversely effects the yield of hydroxyaromaticacid resulting from the carboxylation of the phenate. As is shown inEquation 1 the alkali metal phenate reacts with water to yield phenoland alkali metal hydroxide.

1. OM OH 1120 MOH When excess alkalimetal hydroxide is present duringthe carboxylation, it reacts with the carbon dioxide to form thecorresponding carbonate and water, and the water formed then hydrolyzesthe phenate as is shown in Equations 2 and 3 mo MOH The overall reactionthat takes place when alkali metal hydroxide reacts with carbon dioxideand alkali metal phenate is represented by Equation 4 4. 0M OH.

Since phenol is not carboxylated underthe conditions of the Kolbereaction, the yield of hydroxyaromatic acid is reduced when excessalkali metal hydroxide. and/or water-is present-in the alkali metalphenate that iscarboxylated. ln the commercial operation of the Kolbeprocess, the phenol is usually recovered and used in the preparationofadditional amounts of alkali metal-phenate.

In accordance with this invention, a procedure has been developed forthe accurate and rapid determination of the amount of excess alkalimetal hydroxide that is present in the aqueous alkali metal phenatesolution that is used as the spray dryer feed solution. When this methodof determining thealkalinity of the solution is used, adjustments in therelative amounts of the reactants'that are used can be made rapidly, andas little .as .0 to 0.5 molar percent excess alkali metal hydroxide maybe .used withoutdangerof decomposition and discoloration of the productoccurring during the spray drying operation. As the result of the use ofthese uniform small .excesses of alkali metal hydroxide, the spray-dried.alkalimetal phenatewhich is substantially anhydrous can be carboxylatedtogive improved yields of the corresponding hydroxyaromatic acid.

The novel method of controlling the alkalinity of alkali phenatesolutions is based on theobservation that the excess alkali metalhydroxide in the alkali metal phenatesolution reacts with carbon dioxideinthe drying gas according ,to the following equation:

5. 2MOH CO2 --b MzCO; H2O

In this method, the difference between the carbon dioxidehydroxyaromatic acid that is obtained when the alkali metal content ofthe gas that enters the spray dryer and thatofthe gas that leaves thespray dryer is used as a measure of the amount of alkali metal hydroxidethat is present in the alkali metal phenate feed solution.

When drying gas having a known and uniform carbon dioxide content isintroduced into the spray dryer, there is a direct correlation betweenthe carbon dioxide content of the exit gas and the alkalinity of thefeed solution. By determining the carbon dioxide content of the exit gascontinuously or at frequent intervals and then adding the amount ofphenol or alkali metal hydroxide to the feed solution that is necessaryto keep the carbon dioxide content of the exit gas within apredetermined range, it is possible to maintain the alkalinity of thefeed solution within the range of to 0.5 molar percent, and preferablywithin the range of 0.05 to 0.3 molar percent.

In the practice of this invention, an aqueous alkali metal phenatesolution is spray dried by the process described in US. Pat. applicationSer. No. 584,576 During the spray drying, samples of the exit gas aredrawn continuously or periodically from the exit gas stream andoptionally from the inlet gas stream and fed to a gas analyzercalibrated to give readings of 0 to 0.5 percent of carbon dioxide. Whengas of known carbon dioxide content, such as air, is being introducedinto the spray dryer, the measurement of the carbon dioxide content ofthe inlet gas is usually omitted. For each set of reaction conditionsbeing used, which include, for example, the salt being dried, theconcentration of the feed solution, the spray drying conditions, thecarbon dioxide content of the inlet gas, and the like, a correlation isestablished between the carbon dioxide content of the exit gas and theamount of excess alkali metal hydroxide or phenol in the feed solution.Such a correlation may be established by analyzing samples of the feedsolution during spray drying and equating their analyses with the carbondioxide content of the exit gas at the time the samples were taken. Atypical correlation between the phenol or sodium hydroxide content of asodium phenate feed solution and the carbon dioxide content of the gasleaving the spray dryer is shown in the following table. The gasintroduced into the spray dryer during this run contained about 0.055percent of carbon dioxide.

Percent Percent excess excess NaOH phenol Percent. CO1 in exit gas:

In the practice of this invention, following the determination of theamount of excess phenol or alkali metal hydroxide that is present in thefeed solution, sufficient phenol or alkali metal hydroxide is addedautomatically or manually to the feed solution to bring the carbondioxide content of the exit gas to the preferred range of about 0.01percent to 0.025 percent, which corresponds to about 0 to 0.2 percent ofexcess alkali metal hydroxide in the feed solution.

While the process of this invention is of particular value in theproduction of sodium phenate, which is used commercially in thepreparation of salicylic acid, it can also be used in the production ofother alkali metal salts, including alkali metal phenates and alkalimetal carboxylates. The phenols whose alkali metal salt solutions may beused as the starting materials in the novel method of this invention maybe any mononuclear or polynuclear aromatic compound containing at leastone hydroxyl group substituted in the aromatic nucleus. They may alsohave other nuclear substituents such as alkyl groups. halogen atoms,amino groups, nitro groups,

and the like. Illustrative of these phenols are the following: phenol,o-, m-, and p-cresols, p-aminophenol, m-nitrophenol, 2,4-dichlorophenol,pentachlorophenol, l -naphthol, 2 naphthol,, 5 -amino-l -naphthol,4-nitro-l-naphthol, l-chloro- Z-naphthol, and the like. The acids whosealkali metal salt solutions may be used in the practice of thisinvention include a wide variety of monocarboxylic and polycarboxylicaliphatic and aromatic acids, such as hexanoic acid, decanoic acid,citric acid, ethylenediamine tetraacetic acid,hydroxymethylethylenediamine triacetic acid, benzoic acid, phthalicacid, tetrachlorophthalic acid, salicylic acid, sulfosalicylic acid,toluenesulfonic acid, and the like. Sodium and potassium are the mostcommonly used and the preferred alkali metal constituents of the salts;salts of other metals of Group 1 A of the Periodic Table of the elementsmay also be used, if desired, in the process of this invention.

The aqueous alkali metal salt solution that is used as the feed to thespray dryer comprises from about 50 percent to 75 percent by weight ofone or more of the aforementioned alkali metal salts and from about 25percent to 50 percent by weight of water. As is well known in the art,the aqueous salt solutions may be prepared by reacting a phenoliccompound or carboxylic acid in solid state, in molten state, or insolution or suspension in a suitable liquid with an alkali metalhydroxide which may also be in the solid state, in solution, or insuspension. For example, the solution may be prepared by dissolving aphenol or carboxylic acid in a concentrated aqueous solution of analkali metal hydroxide.

As is disclosed in U.S. Pat. application Ser. No. 584,576 the spraydrying of alkali metal salts can be carried out in conventional spraydrying equipment. Spray dryers generally consist of a means of atomizingthe liquid feed, a source of hot gas, a drying chamber, and a means ofseparating the dry product from the exhaust gases. The spray dryer maybe operated with concurrent or countercurrent gas flows. The use of acountercurrent drying gas flow is preferred for the present purposes.

The drying gas that is used in this process must contain not more thanabout 0.5 percent by volume of carbon dioxide, since when greateramounts of carbon dioxide are present reactions which occur between thealkali metal salt and carbon dioxide yield undesirably byproducts, suchas unstable alkali metal phenylcarbonate, which burns in the presence ofoxygen. Consequently, both the yields and the quality of the product areadversely affected by the presence of more than about 0.5 percent byvolume of carbon dioxide in the gas stream. Air and other inert gasesthat contain less than about 0.5 percent by volume of carbon dioxide maybe effectively employed as the drying gas in the spray drying step.

In most cases the drying gas enters the drying chamber of the spraydryer at a temperature within the range of about 500 to 900 F. Theoutlet temperature of the drying gas will range from about 230 to 300 F.It will be understood, however, that the exact temperature of the dryinggas is not critical, since the required temperature need only be highenough to obtain the desired degree of dehydration and will depend inpart upon the residence time of the drying gas in the drying chamber.For most purposes the residence time will vary from about 5 to 30seconds. When a hotter drying gas stream is em ployed, the residencetime may be still shorter. In all cases the outlet temperature of thedrying gas must be maintained below the decomposition temperature of theparticular alkali metal phenate being treated. The spray drying step isordinarily carried out under ambient pressure conditions.

Any of the commercially available gas analyzers that are capable ofreporting carbon dioxide contents in the range of 0 to L0 percent can beused in the practice of this invention. For example, a Beckman lRAnalyzer Model 315 has been used in combination with a Honeywell SinglePen Strip Chart Recorder to measure the alkalinity of spray dried sodiumphenate.

The invention may be more clearly understood when it is considered inconjunction with the attached drawing. This drawing illustratesschematically an apparatus in which a preferred embodiment of theprocess of this invention may be carried out. a

.As is shown in the drawing, feed tank 11 contains an aqueous solutioncomprising 65 percent by weight of sodium phenate and a 0.! to 0.3 molarpercent excess of sodium hydroxide. This solution 12 was prepared byadding an appropriate amount of phenol to weigh tank 13 and anappropriate amount of a 50 percent aqueous sodium hydroxide solution toweigh tank 14 and mixing the phenol and aqueous sodium hydroxidesolution in mix tank 15 before adding the resulting solution to feedtank 11. The aqueous sodium phenate solution 12, which was maintained ata temperature of about 200 F. to prevent its solidification in theunheated feed lines, was fed through line 16 to centrifugal atomizer 17,

which atomized the feed in a horizontal plane. The droplets of feedsolution fell continuously into chamber 18. Line 19 delivered aircontaining about 0.05 percent by volume of carbon dioxide which had beenheated to about 575 F. into chamber 18, and the heated aircountercurrently contacted the aqueous sodium phenate droplets andcaused them to dry, thereby producing finely divided sodium phenateparticles having a particle size range of from about 10 to 110 microns,an average particle size of less than about 70 microns, and a watercontent of less than about 2 percent by weight. The

sodium phenate powder was collected in container 20. Outlet air at atemperature of about 250 F. which contained some entrained sodiumphenate particles was passed through line 21 into a cyclone separator 22and the sodium phenate particles were collected in container 20a The airwas passed through line 23 by means of fan 24 into a water scrubber 25and cooled before being returned to the process through line 26.Nitrogen was added to the gas through line 27 to replace gas lost duringthe spray drying process. The gas stream was passed through heater 28using fan 29 before it was returned to chamber 18. During the processsamples of the exit gas were withdrawn from line 23 through line 30 bymeans of vacuum pump 31 into CO analyzer-recorder 32. Optionally,samples of the inlet gas were withdrawn from line 19 through line 33 bymeans of vacuum pump 34 into the CO analyzer-recorder 32.

Whenever the gas analyzer 32 indicated that the carbon dioxide contentof the exit gas was not in the range of about 0.010 percent to 0.025percent, sufficient phenol or sodium hydroxide was added to weigh tanks13 or 14 to bring the carbon dioxide content of the exit gas to thisrange.

The spray drying apparatus schematically shown in thedrawing correspondsto a Nerco-Niro Spray Dryer Model M- 260 This apparatus, operated in theabove-described manner, produced about 1100 pounds per hour of sodiumphenate that contained 0.1 molar percent to 0.3 molar percent of sodiumhydroxide and about 0.1 percent by weight of water when a residence timein chamber 18 of about 10 seconds was used. When this sodium phenate wascarboxylated, salicylic acid was obtained in a conversion of 88 percentand a yield of 94 percent.

In the hereinbefore described process, the gas leaving the spray dryeris passed through a cyclone separator and a water scrubber before it isrecycled. Nitrogen is added to the gas stream to replace gas lost duringthe spray drying process. Sufficient air enters the system through leaksin the equipment to maintain the carbon dioxide content of the inlet gasat about 0.055 percent by volume.

In another preferred embodiment of the process, the drying gas which hasbeen heated to a temperature in the desired range is passed into thespray dryer. The exit gas is passed through a cyclone separator andwater scrubber and is then discarded. When the drying gas is notrecycled, it is preferred that the carbon dioxide contents of both theinlet gas and the exit gas be measured so that an accurate determinationcan be made of the amount of carbon dioxide that has reacted with theexcess phenol or alkali metal hydroxide in the feed solution.

The terms and expressions that have been used are used as terms ofdescription and not of limitation. There is no intention in the use ofsuch terms and expressions of excluding any equivalents of the featuresshown and described or portions thereof. it is recognized that variousmodifications are possible within the scope of the invention claimed.

Iclaim:

1. In the process for the production of substantially anhydrousparticles of an alkali metal phenate which comprises atomizing anaqueous solution containing about 50 percent to percent by weight ofsaid salt, contacting the resulting spray with a stream of inert gascontaining less than about 0.5 percent by volume of carbon dioxide andheated to a temperature in the range of about 500 F. to 900 F. for thetime required to effect dehydration and solidification of the alkalimetal salt in said spray, and separating substantially anhydrous, finelydivided particles of said alkali metal salt from said inert gas stream,the improvement wherein the alkalinity of the aqueous alkali metal saltsolution is maintained within the range of 0 to 0.5 molar percent bymeasuring the carbon dioxide content of the inert gas leaving the spraydryer and adding to the aqueous alkali metal salt feed solution theamount of alkali metal hydroxide necessary to maintain the carbondioxide content of said inert gas within a predetermined range.

2. The process of claim 1 wherein the alkali metal phenate is 0 sodiumphenate.

3. The process of claim 1 wherein the alkalinity of the aqueous alkalimetal phenate solution is maintained within the range of 0.1 molarpercent to 0.3 molar percent.

4. The process of claim 1 wherein the carbon dioxide content of theinert gas leaving the spray dryer is continuously monitored.

5. The process of claim 1 wherein the carbon dioxide contents of theinert gas entering the spray dryer and of the inert gas leaving thespray dryer are measured and the difference between these carbon dioxidecontents is used as an index of the alkali metal hydroxide content ofsaid spray dryer feed solution.

6. The process of claim 5 wherein the difference between the carbondioxide content of the inert gas entering the spray dryer and that ofthe inert gas leaving the spray dryer is used to control the flow ofalkali metal hydroxide into said spray dryer feed solution.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,554,265 Dated Jan. 1.2, 197].

Inventor(s) Gonzalo D. Milian It is certified that error appears in theaboveidentified patent and that said Letters Patent are hereby correctedas shown below:

Column 1, Item 72, The inventor's address should read --HasbrouckHeights, N.J.--.

Signed and sealed this 20th day of April 1971.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JP

EDWARD M.FLETGHER,JR.

Commissioner of Patents Attesting Officer-

2. The process of claim 1 wherein the alkali metal phenate is sodiumphenate.
 3. The process of claim 1 wherein the alkalinity of the aqueousalkali metal phenate solution is maintained within the range of 0.1molar percent to 0.3 molar percent.
 4. The process of claim 1 whereinthe carbon dioxide content of the inert gas leaving the spray dryer iscontinuously monitored.
 5. The process of claim 1 wherein the carbondioxide contents of the inert gas entering the spray dryer and of theinert gas leaving the spray dryer are measured and the differencebetween these carbon dioxide contents is used as an index of the alkalimetal hydroxide content of said spray dryer feed solution.
 6. Theprocess of claim 5 wherein the difference between the carbon dioxidecontent of the inert gas entering the spray dryer and that of the inertgas leaving the spray dryer is used to control the flow of alkali metalhydroxide into said spray dryer feed solution.